The invention relates to a process for preparing optically active phenyl glycine, that is D-phenyl glycine and/or L-phenyl glycine. D-phenyl glycine is useful as a starting material for the preparation of the antibiotic .alpha.-aminobenzyl penicillin, while L-phenyl glycine is useful for the preparation of the sweeting agent L-asparagine-L-phenyl glycine alkyl ester.
Phenyl glycine has been resolved by treatment of racemic phenyl glycine with optically active camphor sulphonic acid, as disclosed in the Journal of American Chemical Society, volume 47, page 1170 (1925). The racemic phenyl glycine is usually prepared by hydrolysis of the corresponding nitrile by treating the nitrile with large excesses of strong acid, such as, e.g., hydrochloric acid, as disclosed in the Journal of American Chemical Society, volume 42, page 2264 (1920).
The disadvantage of the aforementioned procedure for preparing optically active phenyl glycine from the racemic precursor nitrile is the large amount of salts that are produced as by-products, since, after hydrolysis of the nitrile, the hydrolysis mixture must be neutralized with, e.g. ammonia, for the recovery of the phenyl glycine.
In accordance with the invention, it has been discovered that optically active camphor sulphonic acid is not only suitable for effecting the optical resolution of racemic phenyl glycine, but is also suitable for hydrolyzing phenyl glycine amide to phenyl glycine without losses of optical activity. Thereby, much less neutralized acid in the salt form, is obtained as a by-product.